The long term goal of the study is to understand the role of androgens and/or estrogens in regulating functions of the efferent ductules (ED) and epididymis (EP) in sperm maturation. The aim of the present study is to test the hypothesis that androgens, or estrogens, or both are important for expression of the androgen receptor (AR) and estrogen receptor (ER) genes and/or proteins. The up-or down-regulation of expression may depend upon the region, the cell type, and the state of growth of the ED and EP. To test the hypothesis we propose to characterize mRNAs and proteins for AR and ER at the molecular subcellular levels in different regions of the ED and EP of mature animals (Exp. 1), immature growing animals (Exp. 2), mature castrated animals with or without substitution of androgens or estrogens or both (Exp. 4). The reverse transcriptase polymerase chain reaction technique will be used to identify mRNA transcripts, and in situ hybridization will be used to localize mRNA at the subcellular level. Immunohistochemical and Western blotting techniques will be used to identify AR and ER proteins. Changes in mRNAs and proteins will be related with those in structural morphometry and hormonal profiles (testosterone, estrogen, and luteinizing hormone). Whereas results of the first two experiments will provide semiquantitative data on gene/protein expression for AR and ER as a function of the region and development, those from the latter two experiments will provide semiquantitative data on differential significance between androgens and estrogens as well as between circulating factors and testicular factors in regulating AR and ER gene/protein expression. Overall, results will provide insights on regulation of the ED and EP which are functionally important in sperm maturation and, thus, in male fertility.